Metadata

name: bevy-dialogue-system
description: Bevy 0.20 dialogue data: line tables in a resource, the current line index on a component, and choice flags filtered before the write. Use when lines or choices advance. Keywords: Bevy, dialogue, line index, choices, ECS.

Bevy dialogue system

When to use

Load this when lines, choices, or speaker ids advance. Rendering the line is bevy-ui-text.

ECS shape

Components: a line id and a speaker id that you define.
Resources: run-wide tables live in a resource (bevy-data-resources), not an autoload.
Systems: mutate those components on Update or the fixed timestep. Use .chain() when damage must land before death.
Messages: one-shot facts (hit, pickup, quest advance) go through bevy-events-messaging. This file does not add a new event type name.

Engine counterparts

Godot idea	Bevy idiom
Line table	A resource of ids and strings.
Current line	A component that stores the line index.
Portrait	An image handle via bevy-asset-scenes. Layout is bevy-ui-layout.

Scope

Dialogue data is a resource of lines plus a component that stores the current line index. Rich text rendering belongs on bevy-ui-text.

[dependencies]
bevy = "0.20"

#[derive(Clone)]
struct LineDef {
    speaker: &'static str,
    text: &'static str,
    next: Option<usize>,
}

#[derive(Resource)]
struct DialogueTable {
    lines: Vec<LineDef>,
}

#[derive(Component)]
struct LineMark {
    index: usize,
    open: bool,
}

fn advance_line(
    keys: Res<ButtonInput<KeyCode>>,
    table: Res<DialogueTable>,
    mut marks: Query<&mut LineMark>,
) {
    if !keys.just_pressed(KeyCode::Space) {
        return;
    }
    for mut mark in &mut marks {
        if !mark.open {
            continue;
        }
        let Some(line) = table.lines.get(mark.index) else {
            mark.open = false;
            continue;
        };
        match line.next {
            Some(next) => mark.index = next,
            None => mark.open = false,
        }
    }
}

fn spawn_conversation(mut commands: Commands) {
    commands.insert_resource(DialogueTable {
        lines: vec![
            LineDef {
                speaker: "guide",
                text: "The gate opens at dusk.",
                next: Some(1),
            },
            LineDef {
                speaker: "guide",
                text: "Bring the key.",
                next: None,
            },
        ],
    });
    commands.spawn(LineMark {
        index: 0,
        open: true,
    });
}

pub struct DialoguePlugin;

impl Plugin for DialoguePlugin {
    fn build(&self, app: &mut App) {
        app.add_systems(Startup, spawn_conversation)
            .add_systems(Update, advance_line);
    }
}

Choices are data on the line. Hide a choice when its required flag is absent.

#[derive(Clone)]
struct ChoiceDef {
    label: &'static str,
    next: usize,
    requires_flag: Option<&'static str>,
}

#[derive(Resource)]
struct ChoiceList {
    choices: Vec<ChoiceDef>,
}

#[derive(Resource, Default)]
struct StoryFlags {
    names: Vec<&'static str>,
}

#[derive(Component)]
struct LineMark {
    index: usize,
}

fn shown_choices(flags: &StoryFlags, list: &ChoiceList) -> Vec<usize> {
    list.choices
        .iter()
        .enumerate()
        .filter_map(|(index, choice)| match choice.requires_flag {
            Some(flag) if !flags.names.iter().any(|name| *name == flag) => None,
            _ => Some(index),
        })
        .collect()
}

fn choose_first(
    keys: Res<ButtonInput<KeyCode>>,
    flags: Res<StoryFlags>,
    list: Res<ChoiceList>,
    mut marks: Query<&mut LineMark>,
) {
    if !keys.just_pressed(KeyCode::Digit1) {
        return;
    }
    let Some(choice_index) = shown_choices(&flags, &list).first().copied() else {
        return;
    };
    let next = list.choices[choice_index].next;
    for mut mark in &mut marks {
        mark.index = next;
    }
}

fn open_choice(mut commands: Commands) {
    commands.spawn(LineMark { index: 0 });
}

pub struct ChoicePlugin;

impl Plugin for ChoicePlugin {
    fn build(&self, app: &mut App) {
        app.insert_resource(StoryFlags {
            names: vec!["has_key"],
        })
        .insert_resource(ChoiceList {
            choices: vec![
                ChoiceDef {
                    label: "Open the gate",
                    next: 2,
                    requires_flag: Some("has_key"),
                },
                ChoiceDef {
                    label: "Leave",
                    next: 3,
                    requires_flag: None,
                },
            ],
        })
        .add_systems(Startup, open_choice)
        .add_systems(Update, choose_first);
    }
}

Expert Knowledge Delta

Target: Bevy 0.20+.

Core ECS types: Component, Resource, Query, Commands, Startup, Update, Fixed / FixedMain (bevy::time), .chain(), Plugin, DefaultPlugins, MinimalPlugins. Messages and observers are an ownership slot. See bevy-events-messaging for their APIs. Systems run in parallel unless .chain() orders the ones that conflict.

Who owns state

Piece	Owner	Who may mutate	Schedule
Data on one entity	`Component`	One system via `Query`	`Update` or `FixedMain`
One value for the whole app	`Resource`	One system	`Startup` to insert, then the schedule that reads it
Spawn	`Commands`	The spawning system	`Startup` for the initial world; later schedules for runtime spawn
Order that must not race	`.chain()`	The chained systems only	Same schedule
Plugin boundary	`Plugin`	`build` registers systems and resources	Before the app runs

Borrow rule: two systems that both mutably query the same component must be ordered (.chain()) or split so only one writes. Unrelated systems stay parallel. That is the ECS page rule, not a guess at a system-set API.

Decision

If you need	Do this	Do not
Per-entity data	`Component` + `Query`	A Godot node script
App-wide config or clock	`Resource`	Copy the value onto every entity
Stable simulation step	`FixedMain` and the `Fixed` clock	Tie simulation to raw frame `Update`
Startup spawn	`Commands` in `Startup`	Spawn from a render system
Cross-system notice that is not shared state	Message or observer slot in `bevy-events-messaging`	A new event type invented in this file
An API outside this skill	Load the skill that owns it	A made-up crate or API

Load references/ecs-ownership.md for the ownership table.

NEVER

Do not pin /0.20.0/ in docs URLs. WHY: links stay on latest; the 0.20 target is stated once in prose.
Do not mutably query the same component from two unordered systems. WHY: the schedule runs systems in parallel unless .chain() orders them.
Do not copy the line table onto every speaker. WHY: the table is one resource; the line index is the per-conversation component.
Do not invent a physics, navigation, networking, or XR crate here. WHY: this skill only names documented Bevy crates and modules.
No Godot node, resource, or signal types for this mechanic. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.
No Godot types in Bevy code. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.
No invented APIs or unnamed third-party crates as the chosen solver. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

Reference

The library pin on bevy-master stays 0.20.0. Official pages stay on the unversioned site.

Official Documentation

ECS - Component, systems, Query, Startup, Update, and .chain().
Plugins - Plugin, DefaultPlugins, MinimalPlugins, and add_plugins.
Examples - Example tree on the latest branch.

Related Skills

Prerequisites

bevy-master - Hub and schedules.
bevy-ecs-composition - Components and systems.
bevy-ui-text - Draw the line.
bevy-quest-system - Quest gates.
bevy-data-resources - Tables and definitions.
bevy-events-messaging - One-shot facts.

Complements

bevy-state-machines - Mode flags.
godot-dialogue-system - Equivalent Godot skill.

Downstream / consumers

None yet.

Master

bevy-master - Bevy router.

bevy-dialogue-system

安装技能